1. Field of the Invention
The present invention relates generally to hydraulic control apparatuses for automatic transmissions, and particularly to a hydraulic control apparatus for an automatic transmission suitably configured to suppress shock during shifting (shift shock).
2. Description of Background Art
FIG. 5 of the present application is a systematic diagram illustrating a hydraulic control apparatus for a hydraulic multiple disk clutch according to the background art. There are provided a 1st speed clutch 44, a 2nd speed clutch 65, and a 3rd speed clutch. A working fluid for each clutch is fed from a working fluid inlet port 110 to a valve body 90, in which its destination is determined. A linear solenoid valve 114 is a valve that controls the supply and interruption of the working fluid to an emergency valve 115. The emergency valve 115 normally feeds the working fluid to a 1-2 speed changeover valve 117; however, when the linear solenoid valve 114 fails to stop in an interrupting state, the emergency valve 115 is switched so that the working fluid is fed to the 1-2 speed changeover valve 117 with the linear solenoid valve 114 being bypassed.
A 1-2 speed selector solenoid 116 is provided to operate the spool 124 of the 1-2 speed changeover valve 117 for the supply and interruption of the working fluid. The 1-2 speed changeover valve 117 feeds the working fluid supplied from the linear solenoid valve 114 to either the 1st speed clutch 44 or a 2-3 speed changeover valve 119 in response to the position of the spool 124.
A 2-3 speed selector solenoid 118 is provided to feed or interrupt hydraulic pressure adapted to drive the spool of a 2-3 speed changeover valve 119. The 2-3 speed changeover valve 119 feeds the working fluid supplied from the 1-2 speed changeover valve 117 to either the 2nd speed clutch 65 or the 3rd speed clutch 66.
Hydraulic control valves 120 and 121 are provided to control discharge of the return oil from the hydraulic multiple disk clutches. The above-described hydraulic control apparatus for an automatic transmission is disclosed in Japanese Patent Laid-Open No. 2003-139167.
The hydraulic control apparatus for an automatic transmission described in Japanese Patent Laid-Open No. 2003-139167 has only one hydraulic control valve 121 serving as a valve that alleviates shift shock for the 2nd speed clutch 65 and 3rd clutch 66. This is because the valve 121 is actuated to drain the working fluid moderately, only when an upshift is implemented to change the first speed ratio to the second speed ratio or the second speed ratio to the third speed ratio. On the other hand, when a downshift is implemented, the valve 121 is prohibited from being actuated while placing priority on quickly draining the working fluid.
For a twin clutch of a multi-stage automatic transmission; however, two clutches are designed to operate both the upshift and downshift. It is desirable, therefore, that a hydraulic control valve, i.e., an orifice control valve be arranged to operate two clutches.